Superparamagnetic Adsorbent Based on Phosphonate Grafted

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Superparamagnetic adsorbent based on phosphonate grafted mesoporous carbon for uranium removal Syed M. Husnain, HyunJu Kim, Wooyong Um, Yoon-Young Chang, and Yoon-Seok Chang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01737 • Publication Date (Web): 07 Aug 2017 Downloaded from http://pubs.acs.org on August 13, 2017

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Industrial & Engineering Chemistry Research

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Superparamagnetic adsorbent based on phosphonate grafted

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mesoporous carbon for uranium removal

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Syed M. Husnain a,b , Hyun Ju Kim b ,Wooyong Um a,b , Yoon-Young Chang c

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and Yoon-Seok Chang a,*

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a

Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea

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b

Division of Advanced Nuclear Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea

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c

Department of Environmental Engineering, Kwangwoon University,

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Seoul 139-701, Republic of Korea

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* Corresponding author: Tel.: +82-54-279-2281; Fax: +82-54-279-8299;

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E-mail: [email protected]

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Abstract

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A direct approach was presented to graft phosphonate groups on magnetic mesoporous

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carbon by an impregnation method with environmentally friendly precursors unlike the

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conventional methods involving series of complicated steps and harsh conditions. Through

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the in situ reduction of Fe3+, magnetite particles of ~10 nm were successfully embedded into

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the mesopores, which was confirmed by HR-TEM. Surface characterization by XPS and

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FTIR revealed that the phosphonate functional groups anchored through multi-dentate

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bonding with the surface of P-Fe-CMK-3. Due to the combined advantages of mesoporous

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pore size (5.5 nm), phosphonate ligands (1.42 mmol g-1), and magnetic sensitivity (5.20 emu

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g-1), this multifunctional adsorbent captured > 85% of UO22+ within five minutes and the

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maximum adsorption capacity was 150 mg g-1 at pH 4. The exceptionally high selectivity and

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efficiency of P-Fe-CMK-3 towards uranyl capture even in groundwater (Kd = 1 × 105 mL g-1),

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radioactive wastewater (Kd = 3 × 104 mL g-1) and seawater (Kd = 1 × 104 mL g-1) at V/m =

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1000 mL g-1 was better than that of the previously reported adsorbents. Importantly, the

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adsorbent maintained UO22+ adsorption efficiency > 99% over five cycles due to the excellent

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chemical and structural stabilities. Above all, the adsorbent could be manipulated for UO22+

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capture with help of a magnetic field in the real world, especially in case of nuclear accidents,

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decommissioning of nuclear power plants, and/or uranium recovery from seawater.

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Key words: Uranium, superparamagnetic adsorbent, radioactive material, phosphonic acid,

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mesoporous carbon

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TOC

46 47 48 49 50 51 Groundwater

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Seawater

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Radioactive wastewater 0

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50

100

U Sorption Efficiency (%)

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Introduction

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As the heart of nuclear energy, uranium is the most abundant primordially occurring

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natural actinide. It has a pivotal importance in the nuclear fuel cycle as a source of energy as

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well as radioactive waste. It has a very long half-life (~4.5 billion years) and slowly decays

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by emitting α particles.1 Hexavalent uranium (U6+) and tetravalent uranium (U4+) are the two

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predominant oxidation states of uranium in the environment due to leaching from natural

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deposits, mine tailings, emissions from nuclear facilities and uranium-containing phosphate

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fertilizers.2 In most of radioactive wastewater at low pH, it exists as uranyl (UO22+) ion with

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significant mobility and propensity to enter the food chain. According to hard soft acid base

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(HSAB) sense, uranyl is regarded as a hard cation due to small size, high positive oxidation

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state and a low polarizability, which readily reacts with nucleotides and proteins due to its

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high affinity for hydroxyl, carboxyl, and phosphate groups.3, 4 Acute exposure to uranium can 3 ACS Paragon Plus Environment


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induce health concerns including reproductive, renal, developmental, DNA, and brain

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damages.5 Many cases of chronic kidney disease and several types of cancer have been

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diagnosed in the inhabitants of Sri Lanka and South Carolina due to the consumption of

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uranium-contaminated groundwater.6, 7 As a result of its chemical and radio toxicities, the

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U.S Environmental Protection Agency (EPA) and the World Health Organization (WHO)

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have recommended the maximum contaminant level (MCL) for uranium around 30 ppb in

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drinking water.8 On the other hand, approximately 4 billion tons of uranium is naturally

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present in world oceans with average uranium concentration of ~3 ppb, which could be used

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for nuclear fuel for many years.9 Therefore, it is very important to capture and extract

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uranium for multiple benefits.

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Over the years, several remediation methods have been opted to recover uranium from

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nuclear waste including solvent extraction10, co-precipitation11, membrane filtration12,

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reductive precipitation13, and ion exchange/adsorption.14 Among these, the magnetic assisted

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chemical separation (MACS) is based on adsorption phenomenon in which magnetic micro

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particles (MMPs) are coated with solvent extractant to selectively recover radionuclides and

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toxic metals from industrial effluents.15 In this context, various adsorbents such as Cyanex

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923@MMPs16,

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DMDBTDMA@MMPs20 have been reported for aqueous uranium removal. However, these

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coated MMPs have small surface area (< 30 m2 g-1) and they are unable to sustain in acidic

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and radiation environments, resulting in low sorption capacity and secondary waste due to

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leaching of iron and coating materials.18, 21 Moreover, most of these adsorbents are tested in

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deionized water (DIW), which does not reflect the complex conditions of the real

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environment.

D2EHPA@MMPs17,

TOPO@MMPs18

CMPO@MMPs19,

and

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Magnetic mesoporous carbons (MMCs) have aroused great interest recently because they

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combine the properties of both the mesoporous carbon materials and the magnetic 4 ACS Paragon Plus Environment

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nanomaterials, such as high surface area, tunable pore size, outstanding thermal and chemical

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stabilities, excellent biocompatibility, superparamagnetism, and the Néel relaxation effects.22,

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23

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guided drug delivery systems24, electromagnetic shielding25, magnetically recyclable

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adsorbents23, 26, and carriers for precious metal catalysts.27 However, due to the hydrophobic

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characteristic of MMCs they do not disperse well in water and adsorb mostly the organic

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pollutants.28 These issues can be tackled by the introduction of proper functional groups

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which can enhance the dispersibility and capability to remove a wide range of contaminants

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in aqueous media. Recent studies demonstrated that mesoporous carbons with different

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functional groups, i.e., the oxime29, phosphoryl30, and carboxyl31 could be used as adsorbents

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for uranium. Among the reported functionalities, most of them suffer from complex synthesis

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protocols, toxic nature of chemicals, long preparation time, low product yield, and high cost,

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which limit the use of such adsorbents. In addition, the separation of these adsorbents in the

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open environments is very difficult. In order to overcome the aforementioned challenges, it is

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highly desirable to develop a magnetically retrievable adsorbent that can selectively bind the

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uranium in real environmental waste samples and make the entire remediation processes

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simple, environmentally benign, rapid, and cost effective.

These multifunctional nanomaterials have promising applications including magnetically

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Organophosphorus compounds and their derivatives have been widely employed as

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UO22+ extracting agents due to their excellent coordination ability and stability in the harsh

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environments that are usually encountered in nuclear waste streams.32 In addition,

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phosphonate groups (C–PO(OH)2 or C–PO(OR)2) can be homogeneously incorporated on the

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variety of substrates including metal oxides due to the tendency to form P–O⋯M bonds with

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good hydrolytic stability.33 Motivated by these advantageous qualities, we aimed to

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synthesize the superparamagnetic adsorbent based on phosphonate anchored mesoporous

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carbon by a facile impregnation method. Herein, nitrilotris(methylene)triphosphonic acid 5 ACS Paragon Plus Environment


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(NTMP) was used as a phosphonate precursor; it has industrial application in circulating

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water systems due to its excellent chelating and anti-scaling properties as well as ecologically

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benign nature.34 The prepared P-Fe-CMK-3 magnetic adsorbent was investigated as a

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uranium scavenger with respect to the associated isotherm, kinetics and the effects of pH,

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ionic strength, and reusability. In addition, its extraordinary selectivity towards uranium in

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real environmental solution samples (e.g., groundwater, radioactive wastewater and seawater)

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makes it one of the most powerful magnetic adsorbents ever reported.

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Materials and methods

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Materials

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Pluronic copolymer P123 (EO20PO70EO20, EO = ethylene oxide, PO = propylene oxide),

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NTMP solution (50 wt.% in H2O), Sucrose (99%), anhydrous FeCl3 (97%), and H2SO4 (98%)

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were purchased from Sigma–Aldrich. Ethylene Glycol (99%) and Tetraethyl orthosilicate

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(95%) were procured from Wako Chemicals. All other reagents used in the experiment and

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analysis were of analytical grade. The solutions were prepared with high-purity DIW (18.25

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MΩ cm-1) from a Millipore Milli-Q water purification system.

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Preparation of P-Fe-CMK-3

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First of all, a mesoporous silica, SBA-15 template was prepared as reported elsewhere.35

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Mesoporous carbon (CMK-3) was synthesized using an impregnation method as we

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previously reported.23 To incorporate the Fe3O4 nanoparticles (NPs) into mesopores, 100 mg

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of CMK-3 was added to 40 mL of ethanol solution containing 150 mg of anhydrous FeCl3.

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The resulting mixture was subjected to sonication and magnetic stirring at 60 °C to drive off

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solvent. Then, the impregnated carbon was dried in an oven at 30 °C overnight under

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vacuum. In order to obtain Fe-CMK-3, the prepared carbon powder was wetted by some

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drops of ethylene glycol and heat-treated in nitrogen flow at 510 °C for 1 h at a heating rate 6 ACS Paragon Plus Environment

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of 5 °C min-1. Finally, Fe-CMK-3 was functionalized with phosphonates by stirring in 10 mL

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NTMP solution at 200 RPM for 2 hours using a mechanical shaker. After filtration and

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washing with DIW, the phosphonate-functionalized magnetic mesoporous carbon (P-Fe-

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CMK-3) was dried in an oven at 100 °C for 8 h. In addition, one sample of P-CMK-3 was

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prepared by treating the CMK-3 with NTMP solution under identical conditions. P-Fe-CMK-

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3 adsorbent was prepared in duplicate in 5 different batches. The overall scheme (Figure S1)

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for the synthesis of P-Fe-CMK-3 are presented in the Supporting Information (SI).

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Characterization

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Surface functional groups were analysed by Fourier transform infrared spectroscopy (iS50

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FTIR spectrometer equipped with diamond crystal, Thermo Scientific, USA). X-ray

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diffraction (XRD) patterns were collected on a Rigaku D/MAX-2500 V diffractometer with

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step size of 0.02° and 2θ ranging from 10 to 90°. The detailed methods (Text S1) are

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provided in the SI.

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Adsorption batch experiments

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A series of adsorption experiments were carried out at 25 °C in duplicate along with control

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samples. The initial screening of mesoporous carbon adsorbents at different stages of

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modification was assessed by dispersing 0.01 g of adsorbent into 50 mL of 20 mg L-1 UO22+

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solution (in DIW) in 50-mL propylene tubes at pH 4±0.1 and placed on a rotary agitator for

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24 h. (For more detail, see the Text S2).



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Desorption and regeneration experiments

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In order to regenerate the UO22+-loaded P-Fe-CMK-3 adsorbent, it was dispersed in 10 mL of

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0.5 M HCl solution and placed on a rotary agitator for 30 min. Then it was collected with a

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magnet, washed with DIW, and used for more adsorption experiments.

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Decontamination of environmental samples

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To demonstrate potential application of synthesized P-Fe-CMK-3 adsorbent in the

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decontamination of a complex environmental matrix, U solution was spiked in actual

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groundwater (from Yeoncheon, South Korea), seawater (from Pohang, South Korea), and in

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simulated radioactive wastewater (prepared by modification of previous method).29 The

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physicochemical properties and the composition of each sample are listed in the supporting

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information (Table S1). Breifly, 0.01 g of P-Fe-CMK-3 was added in 15-ml conical

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polypropyelene tube. A 10 mL of uranium spiked environmental solution was introduced in

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each tube and placed on rotary agitator at room temperature in duplicate along with control

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sample. After 4 hours of contact time, adsorbent was separated with magnet, filtered the

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remaining solution and analyzed on ICP-MS for UO22+ concentration.

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Results and discussion

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Characterization

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The TEM images of pristine and phosphonate grafted mesorporous carbons are shown in

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Figure 1a and 1b. The Figure 1c and 1d showed numerous, well dispersed Fe3O4

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nanoparticles (NPs) within the mesoporous carbon in the form of dark spots. However, the

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ordered stripe-like morphology of mesoporous carbon deteriorated to a small extent due to


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the in situ formation of magnetite NPs and additional treatment with NTMP. The average size

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of an encapsulated Fe3O4 NPs was about 10 nm (Figure 1e).

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By comparing the XPS (Figure S2a) survey scans of pristine mesoporous carbon, NTMP and

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P-Fe-CMK-3, it can be seen that the Fe 2p, N 1s, P 2p, and P 2s peaks are all present,

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suggesting that iron, nitrogen, and phosphorous elements are successfully incorporated in the

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P-Fe-CMK-3 adsorbent. However, in order to further investigate the grafting mechanism of

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phosphonate, high resolution XPS scans of P 2p, C 1s, O 1s, N 1s and Fe 2p on P-Fe-CMK-3

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were also recorded (Figure S2b-f). The relative contributions of individual components

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(Table S2) were quantified by a previously reported method.23 For the sake of reliable

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reference, the P 2p XPS spectrum of pure NTMP was collected (Figure S2b). The single P 2p

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peak is located at binding energy EB = 134.2 eV, which corresponds to pentavalent tetra-

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coordinated –PO3H2 acids.36 However, after the anchoring of phosphonate in P-Fe-CMK-3,

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the P 2p peak splits into two components at EB = 133.4 eV and EB = 134.5 eV. The slight

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shift of 0.8 eV towards the lower binding energy compared to pure NTMP indicates the

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deprotonation of terminal –POH groups, which leads to the formation of P-O-Fe bonds and/or

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C-P linkage.37 The peak at EB = 134.5 eV corresponds to the C-O-P bonding between

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magnetic mesoporous carbon and NTMP.37 The spectra of the C 1s peak and the O 1s peak in

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P-Fe-CMK-3 can be deconvoluted into four components and three components, respectively

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(Figure S2c and S2d). The carbon species represent C-C (EB = 284.4 eV), C-P (EB = 285.4

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eV), C-N (EB = 286.2 eV), and COO (EB = 288.9 eV).23 The oxygen species correspond to the

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formation of Fe-O-P and/or Fe-O-H (EB = 531.4 eV), P-OH (EB = 532.6 eV), and C-O-P

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linkage (EB = 533.5 eV).38 The N 1s core level in P-Fe-CMK-3 can be decomposed into two

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separate peaks: protonated amine peak, R3NH+ (EB = 402.4 eV) and deprotonated amine

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peak, R3N꞉ (EB = 400 eV) (Figure S2e).39 The two well resolved characteristic peaks at EB =

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713 eV and EB = 726 eV correspond to Fe 2p3/2 and Fe 2p1/2, respectively (Figure S2f).



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The FTIR spectra of pure NTMP (Figure S3a) displayed the characteristic bands around

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1200-1100 cm-1, 1015 cm-1 and 940 cm-1, which were attributed to the P=O stretching

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vibrations, O-P-O symmetric stretches and the P-O-H asymmetric stretches.34 However, after

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the grafting of phosphonate in P-Fe-CMK-3, a broad band appeared around 1040 cm-1,

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signifying that NTMP anchored through both P=O and P-O terminations with the surface 40,

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as previously indicated by the XPS results.

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The crystal structure and mineral formation of P-Fe-CMK-3 adsorbent was examined using

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x-ray diffraction and the results are shown in Figure S3b. The well-defined diffraction peaks

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located at 2θ regions of 18.2°, 30.3°, 35.6°, 43.3°, 53.8°, 57.3°, 62.8°, and 74.2° are attributed

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to (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3) planes of Fe3O4,

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respectively, which corroborates well with standard magnetite (JCPDS No. 19-0629).23 In

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addition, there is a broad C (0 0 2) diffraction peak centered at 2θ regions of 20°–30°, which

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is ascribed to the mesoporous carbon.41

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The N2 adsorption–desorption isotherm (Figure S3c) of P-Fe-CMK-3 exhibited the typical

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type-IV hysteresis loop at (0.5 ≤ P/P0 ≤ 0.9), suggesting the presence of mesopores. The

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corresponding pore-size distribution derived from the adsorption branch using the Barrett–

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Joyner–Halenda (BJH) method (Figure S3c, inset) displayed a sharp peak in the mesoporous

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range centered on 5.5 nm. The average BET specific surface area (186.77 m2 g–1) and pore

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volume (0.054 cm3 g–1) of P-Fe-CMK-3 are significantly lower than those of the pristine

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mesoporous carbon due to the partial blocking of mesopores by Fe3O4 nanoparticles (Table

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S3).

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The isoelectric point (IEP) of P-Fe-CMK-3, Fe-CMK-3, P-CMK-3, and CMK-3 (Figure S3d)

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were interpreted by measuring the zeta potential (ξ) in solutions of different pHs (1.8 to 10).

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Sample P-Fe-CMK-3 has IEP = 3.2, lower than that of the pristine mesoporous carbon (IEP =


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4.1) with the difference of 0.9 unit, indicating that the surface of P-Fe-CMK-3 is grafted with

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NTMP, which makes it fit to adsorb UO22+ over a broad pH range.

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Previous studies demonstrated the use of magnetization curves for the quantification of

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amounts of organic compounds grafted on the magnetic particles.42 Herein, the saturation

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magnetization strengths (Ms) of Fe-CMK-3 and P-Fe-CMK-3 are found to be 13.86 and 5.20

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emu g-1, respectively (Figure S3e). The difference of 8.66 emu g-1 suggests that the NTMP

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content in P-Fe-CMK-3 is ~62.50 % (w/w). In addition, the P-Fe-CMK-3 adsorbent exhibited

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almost negligible coercivity (Hc) of 1 Oe and remanence (Mr) of ~0.05 emu g-1, which

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signifies the superparamagnetic nature of the adsorbent. Above all, it is clear that P-Fe-CMK-

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3 can be recovered from the solution by exposure to an external magnet (Figure S3e, inset

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photo).

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The TGA thermograms of Fe-CMK-3 and P-Fe-CMK-3 yielded a small weight loss (5-10

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wt.%) below 200 °C, due to physisorbed water molecules (Figure S3f). The TGA data

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inferred the higher thermal stability of P-Fe-CMK-3 than Fe-CMK-3. In addition, the degree

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of phosphonate grafting could be evaluated quantitatively as 1.42 mmol g−1 in the

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temperature range of 200−800 °C.

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Adsorption of U

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The adsorptive capability of four different mesoporous carbon adsorbents towards UO22+ is

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depicted in Figure 2a. The pristine mesoporous carbon (CMK-3) adsorbed relatively less

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UO22+ (10 mg g-1) while the magnetic mesoporous carbon (Fe-CMK-3) was found to be

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inefficient for UO22+ capture, as it adsorbed only 2 mg g-1. This fivefold difference in

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adsorption might be due to the higher IEP of Fe-CMK-3 (4.8) and the loss of complex-

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forming hydrophilic groups during the synthesis at higher temperatures.43 In contrast, a

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substantial increase in UO22+ adsorption (60 mg g-1) was observed after the treatment of Fe-

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CMK-3 by NTMP. The thirtyfold increase in UO22+ adsorption is presumably attributed to 11 ACS Paragon Plus Environment


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the lower IEP (3.2) of P-Fe-CMK-3 as well as the abundant phosphonate, containing

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chelating ligands on its surface. Another striking observation was the excellent adsorption of

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UO22+ (82 mg g-1) by P-CMK-3, which was further confirmed by the incorporation of

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phosphonate groups on the mesoporous carbon resulting in the lowest IEP (2.8). Therefore,

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on the basis of adsorbed UO22+, the synthesized mesoporous carbon adsorbents could be

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arranged in the following order: P-CMK-3 > P-Fe-CMK-3 > CMK-3 > Fe-CMK-3.

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Considering the magnetic sensitivity and the relatively higher UO22+ adsorption, the P-Fe-

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CMK-3 adsorbent was investigated for further UO22+ capture studies.

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Adsorption kinetics

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A small equilibration time is highly desirable in terms of real application of adsorbent

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materials, resulting in a small reactor volume, short operation cycle, and thereby low

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operation and investment costs. Considering these factors, the effect of contact time on the

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adsorption of UO22+ onto P-Fe-CMK-3 was explored to determine the equilibration time

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(Figure 2b). The uptake of UO22+ was ultra-fast, especially in the first few minutes: the

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removal efficiency was >85% in the initial 5 min. The overall sorption process reached a

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steady state within 30 minutes. The equilibration time in this case was much shorter than

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those of 504 h in MPCOF44, 144 h in MMSNs45, and 72 h in S2-LDH.46 To shed light on the

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sorption process, the experimental data were fitted with pseudo-first-order and pseudo-

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second-order kinetic models, respectively (Figure 2b, inset).

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The pseudo-second-order kinetic reaction was the better fitting model due to the higher

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correlation coefficient (R2 = 0.98) which indicates that chemical adsorption is the rate

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limiting step for UO22+ adsorption onto P-Fe-CMK-3.


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Effect of pH

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The solution pH is a major operational factor in sorption process as it affects the solution

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chemistry of metal ions and the charge on the sorbent surface. Adsorption affinity of UO22+

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by P-Fe-CMK-3 over a broad concentration range of HNO3 (2 M to pH = 6.48) is shown in

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Figure 2c. In general, adsorption of UO22+ tends to increase with decrease in acidity. This

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adsorption behavior might be predicted by the pH effect on the entire surface charge of P-Fe-

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CMK-3 and the proton-competitive environment. On the basis of IEP (3.2) of P-Fe-CMK-3,

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when pH < 3.2, the phosphonate functional groups of NTMP were more positively charged

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due to intense competition between protons (H+) and UO22+ for the same binding sites. As a

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result, strong electrostatic repulsion was a major factor for lower retention of UO22+ at lower

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pH. On the contrary, when pH > 3.2, the P-Fe-CMK-3 surface became less positively

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charged, revealing that the phosphonate functional groups were active in adsorbing UO22+.

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Taking into consideration of the acid dissociation constant of NTMP (Figure S4a), when pH
4.48 In addition, the Figure S4b

308

showed the formation of schoepite (UO3·2H2O) precipitates in the pH range of ~5.4-7.2,

309

which could be plausible reason of high sorption capacity at pH > 5. To overcome this issue,

310

further sorption experiments were conducted at pH 4. In general, for any adsorbent, the Kd

311

value > 5 × 103 mL g-1 is considered good and the Kd value > 5 × 104 mL g-1 is considered

312

excellent.49 In our case, the high Kd values, ranged from 8.5 × 103 to 9.9 × 104 mL g-1 in the

313

pH range of 3.68 to 6.48 clearly indicate the effective removal of uranium in acidic and

314

neutral conditions.

315

Effect of ionic strength

316

As environmental solution (such as seawater or radioactive wastewater) involves various

317

ionic species, it is essential to test the effect of ionic strength on UO22+ adsorption. The

318

results (Figure 2d) show a slight decrease of UO22+ adsorption with increase in ionic strength.

319

This small reduction in adsorption might be expected from the competition of Na+ ions with

320

UO22+ for the active binding sites. However, the overall adsorption efficacy of UO22+ was not

321

significantly different at either extreme condition, indicating that the dominant adsorption

322

mechanism would be inner-sphere surface complexation rather than outer-sphere surface

323

complexation or ion exchange process. This postulate would be supported by previous studies

324

which demonstrated that UO22+ adsorption by inner-sphere complexes was independent of

325

ionic strength.50 Therefore, our results predict the formation of stable chelates between

326

phosphonate groups and UO22+ on the surface of P-Fe-CMK-3.


Page 15 of 33

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327

Adsorption isotherm

328

It is essential for understanding the adsorption mechanism, the surface properties, and

329

quantitative comparison of the sorption capacity of different materials.2 To investigate the

330

maximum UO22+ uptake capacity of P-Fe-CMK-3 adsorbent, the equilibrium sorption data

331

were fitted with Langmuir and Freundlich isotherm models, respectively. More details can be

332

found as Text S3 in the SI.

333

Both the models approximated the experimental UO22+ adsorption data well (Figure 2e).

334

However, according to the correlation coefficient (R2) values, it can be seen that there is

335

better agreement between adsorption data and the Freundlich model, indicating that UO22+

336

adsorption can be attributed to multilayer coverage. In other words, the entire adsorbent

337

surface is heterogeneous and there is significant lateral interaction among adsorbed molecules.

338

The maximum UO22+ adsorption capacity (Qmax) of P-Fe-CMK-3 was 150 mg g-1, which is

339

much better than other magnetic adsorbents and comparable to other non-magnetic

340

adsorbents (Table S4).

341

Comparison between radioactive uranium and non-radioactive heavy metals

342

To compare the reactivity of P-Fe-CMK-3 adsorbent between UO22+ and the heavy metals

343

(As5+, Cd2+, Cr6+, Cu2+, Ni2+, Hg2+, Pb2+ and Zn2+), an additional set of experiments was

344

conducted under the identical experiment conditions (Figure 2f). It was found that the P-Fe-

345

CMK-3 adsorbent had higher adsorption affinity towards UO22+ as compared to the other

346

heavy metals. This selectivity was contributed by several factors such as i) HSAB principle

347

which states uranyl is hard acid and prefer to bind hard bases (O over S, N over P)3 , ii) f

348

orbitals of uranium interact more strongly with donor ligands than the d orbitals of the heavy

349

metals51, iii) UO22+ competes with H+ to bond with either P=O or P–O– oxygen atoms within



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Page 16 of 33

350

phosphonate functional groups. The coordinating ability of neutral P=O group arises by the

351

donation of lone pairs of electrons to unoccupied molecular orbitals of UO22+ whereas,

352

negative charge on the P–O– group interacts with UO22+ through electrostatic forces, and iv)

353

UO22+ has a linear structure (O=U=O) unlike the common heavy metals which exists in their

354

divalent forms (M2+) at low pH except As5+, and Cr6+ which predominantly exists in their

355

anionic forms such as H2AsO4- and HCrO4-, respectively So, due to difference in charge and

356

structure, the linear UO22+ ion could be better accommodated by the phosphonate chelating

357

groups and the mesopores in P-Fe-CMK-3.

358

The selectivity coefficient for uranyl ions with respect to competing ions is determined as:

/ =

359

and !"

(1)

360

where !"

361

respectively in the aqueous solution. The coressponding data (Figure 2f , inset) presents

362

desirable selectivity towards uranyl over the range of competing metal ions.

363

Uranium removal from real environmental samples

364

As a result of the excellent UO22+ capture by P-Fe-CMK-3 described above, we investigated

365

the potential applicability of this nano-adsorbent to remediation of natural solution samples

366

spiked with UO22+ (Table S5). The first test was decontamination of groundwater (pH = 7.8)

367

sampled from Yeoncheon, South Korea, which contained diverse ions such as Ca2+ (59 ppm),

368

Na+ (17.6 ppm), Mg2+ (8.3 ppm), K+ (2.7 ppm), Cl− (39 ppm), SO42− (9 ppm), and NO3− (5.4

369

ppm). Here, 948 ppb of UO22+ was spiked in the groundwater sample. Almost 99.1% of

370

UO22+ was removed with an excellent distribution coefficient (Kd = 1.07 × 105 mL g-1).

371

Among natural waters, seawater is one of the most challenging matrices due to its high ionic

are the distribution coefficients for uranyl and competing ions,


Page 17 of 33

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372

strength. The seawater (pH = 8, collected from Pohang, South Korea) contained a very low

373

level of naturally occurring uranium (2.90 ppb) and extremely high contents of common ions

374

such as Ca2+ (400 ppm), Na+ (10,475 ppm), Mg2+ (1,247 ppm), K+ (387 ppm), Cl− (18,800

375

ppm), and SO42− (2,634 ppm). The P-Fe-CMK-3 adsorbent captured up to ~69% of UO22+

376

from seawater within four hours. Moreover, an additional experiment was carried out by

377

adding 450 ppb of UO22+ to similar seawater; the removal efficiency was > 91% with high Kd

378

value of 1.02 × 104 mL g-1. The use of P-Fe-CMK-3 was further extended to UO22+ recovery

379

from radioactive wastewater. The radioactive wastewater (pH = 4) contained Co2+ (119 ppm),

380

Ni2+ (123.6 ppm), Mn2+ (113.7 ppm), Na+ (162.1 ppm), Zn2+ (124.6 ppm), Sr2+ (45 ppm),

381

Cr3+ (85.5 ppm), Cs+ (120 ppm), and UO22+ (290 ppb). Again, P-Fe-CMK-3 showed high

382

adsorption efficacy > 96% with Kd value close to 3 × 104 mL g-1 in 4 h. These UO22+ removal

383

results were far better than those of the previous adsorbents in terms of their application in

384

complex environmental matrices and fast kinetics.

385

Removal Mechanism

386

In general, the removal of metal at the surface of solid sorbent can be predicted due to various

387

probable mechanisms such as surface precipitation, ion exchange, adsorption, co-

388

precipitation, absorption, diffusion, etc. The elemental mapping images showed

389

homogeneous distribution of C, N, O, Fe, P, and U on the surface of UO22+-loaded P-Fe-

390

CMK-3 (Figure 3a), suggesting strong evidence of uranium adsorption. In order to examine

391

the mode of interaction between UO22+ and the P-Fe-CMK-3 at the molecular scale, XPS

392

scans of the P-Fe-CMK-3 after uranium adsorption were collected (denoted as U-P-Fe-CMK-

393

3). The wide XPS scan (Figure 3b) represents the expected components of P-Fe-CMK-3 with

394

the addition of two U 4f peaks, which confirms a significant amount of uranium at the

395

adsorbent surface. The XPS spectra of U 4f can be resolved by a single contribution of



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Page 18 of 33

396

uranium with U 4f5/2 (EB = 393.4 eV) and U 4f7/2 (EB = 382.6 eV), suggesting the absence of

397

redox activity during the adsorption process (Figure 3c).14 After the UO22+ adsorption, the

398

deconvoluted P 2p peaks shift slightly towards lower binding energy (Figure 3d). In addition,

399

a small peak appears at EB = 133.2 eV due to the U-O-P bonding, which is in agreement with

400

the UO22+ adsorption onto tributyl-phosphate-grafted CNTs.52 From Figure 3e, it is noted that

401

the protonated amine (R3NH+) species is more concentrated than deprotonated amine (R3N꞉)

402

on the adsorbent surface due to the synthesis of P-Fe-CMK-3 in the NTMP solution at pH 0.3

403

where R3NH+ is the dominant species (in solution, for amine groups, 9 ≤ pKa ≤12). However,

404

in U-P-Fe-CMK-3, the deprotonated amine peak (R3N꞉) is shifted towards higher binding

405

energy at EB = 400.6 eV with augmented intensity (25.56%). This change could be attributed

406

to the formation of complexes between N(CH2)33- of NTMP and UO22+, in which UO22+

407

shares the electrons with the nitrogen atoms in P-Fe-CMK-3. It is worth noting here that the

408

final pH is always less than the initial pH after the UO22+adsorption, which correlates

409

positively with the increased R3N꞉ peak intensity. Based on the detailed XPS analysis, the

410

uranium adsorption is attributed to the simultaneous interaction of nitrogen and phosphonate

411

functional groups, which promotes the formation of strong complexes with UO22+ on the P-

412

Fe-CMK-3 nanostructure (Figure 4a).

413

Regeneration and reusability

414

The desorption of metal ions from the saturated adsorbents is necessary from economic and

415

industrial perspectives. In the present case, keeping in view of the relatively lower adsorption

416

capability of P-Fe-CMK-3 in extremely acidic conditions, we used a 0.5 M HCl solution to

417

desorb UO22+ from the adsorbent. According to the results (Figure 4b), there was no serious

418

loss in the UO22+ adsorption efficiency (99.67% to 99.16%) over five consecutive adsorption-

419

desorption steps, representing excellent regeneration and reusability. Even after five cycles,


Page 19 of 33

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420

P-Fe-CMK-3 retained its magnetic property and could be retrieved from the solution within 1

421

minute. In addition, the leaching of iron from the adsorbent after a contact time of 24 h in

422

different pH solutions (1 to 10) was nearly 0, suggesting that the iron cores were well

423

protected by the mesoporous carbons. Figure S5 compares the powder XRD data of fresh,

424

adsorbed and regenerated adsorbent after five cycles and no substantial structural changes

425

occurred upon the five cycles which approves adsorbents stability. In addition, the TEM

426

(Figure S6) and the corresponding mapping of individual elements in P-Fe-CMK-3 after five

427

consecutive adsorption desorption runs also attributes to chemical and structural stabilities.

428

429

430

Comparison of P-Fe-CMK-3 with other materials

431

Although numerous studies have been conducted for the effective removal of uranium by

432

various adsorbents as presented in Table S4, the majority of those studies use DIW as the

433

background solution, which does not represent actual environmental characteristics.

434

Therefore, the application potential of those materials in real world is still very limited. In

435

contrast to the previous studies describing high adsorption capacities for UO22+ from trivial

436

aqueous samples, the representative case studies of different adsorbents have been compared

437

(Table S5) in terms of real application and their performance.

438

In general, nano-scale zero valent iron (nZVI) is predominantly used for the remediation of

439

various recalcitrant pollutants including UO22+ in real environmental solutions. However,

440

there are certain issues associated with the nZVI use, such as aggregation, non-reusability,

441

and longer reaction time, i.e., > 10 days for 75% removal of uranium in a concentration range

442

of 20 to 1000 mg L-1 in contaminated water.53 There are several other materials, including 19 ACS Paragon Plus Environment


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Page 20 of 33

443

banana peels nano-sorbent (BPN)54, IRA-910, and Dowex for the UO22+ recovery from mine

444

solutions.55 However, these have low removal efficiency (≤ 70%) and it is difficult to

445

separate them after treatment. Moreover, these materials take longer to reach equilibrium,

446

which may restrict their industrial application. Silica- and zeolites-based materials offer

447

higher retention capability for UO22+, but these materials tend to dissolve easily in alkaline

448

conditions with consequent loss of UO22+ uptake capacity. On the other hand, despite

449

extensive studies, the use of graphene-based adsorbents in the real world is still being debated

450

due to its toxic concern.56 Recently, K2xSn4−xS8−x57, FJSM-SnS58, S4-LDH46, PA/TNTs59,

451

zirconium phosphonates60, CMK-3@PDA61, and Oxime-CMK529 have been reported for

452

effective removal of UO22+. However, most of them are in the form of very fine powder

453

and/or microcrystalline, and thus are unsuitable for the use in membrane or column filtration

454

because they tend to choke filter pores. In addition, these materials have lower adsorption

455

efficiency in real environmental samples. In contrast, the P-Fe-CMK-3 adsorbent is highly

456

selective, magnetically separable, and has excellent recycling efficacy, all of which make it a

457

valuable new method for nuclear waste remediation.

458

459

Conclusion

460

Based on the hard soft acid base (HSAB) concept, the strong UO22+ interaction with the P=O

461

moieties and the persistence of this coordination in harsh acidic and radiolytic conditions, for

462

the first time we presented the synthesis of phosphonate grafted magnetic mesoporous carbon

463

(P-Fe-CMK-3) by the facile impregnation method. The P-Fe-CMK-3 adsorbent selectively

464

retains UO22+ over a broader range of pH levels (pH -0.3 to 6.48) than the existing adsorbents.

465

It also showed maximum adsorption capacity of ~150 mg g-1 at pH 4±0.1, higher than the

466

other adsorbents reported so far. The adsorbent reached a steady state in only 30 minutes and


Page 21 of 33

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467

was easily retrieved in one minute using a magnetic field without causing serious radiation

468

exposure to radiological workers. Above all, the adsorbent was highly effective for the

469

capture of uranyl species from the complex environmental matrices (including radioactive

470

wastewater, groundwater and seawater samples) within a short time (4 h), unlike most of

471

other adsorbents with longer time up to 67 h. The detailed surface analysis by XPS and the

472

insignificant influence of ionic strength suggested that the UO22+ adsorption is due to the

473

synergistic interaction of nitrogen and phosphonate functional groups with the uranium

474

contaminant on P-Fe-CMK-3. Consequently, P-Fe-CMK-3 can be used as a promising

475

adsorbent with ecological benignity, stability and magnetic retrievability for the remediation

476

of uranium from environmental waste solutions.

477 478 479 480 481 482 483

Acknowledgement

484

This work was supported by ‘‘The GAIA Project” by the Korea Ministry of Environment

485

[RE201402059]. This research was also supported by the National Research Foundation of

486

Korea (NRF) grant funded by the Korean government (MSIP: Ministry of Science, ICT and

487

Future Planning) (No. NRF-2016R1D1A1B02013310). The authors also thankful to Dr.

488

Wonseok Kim for providing experimental facility and uranium analysis.

489

Supporting Information

490

Synthesis protocol, experimental design, detailed structural characterization and

491

corresponding results (XPS, FTIR, XRD, BET, PSD, ξ-potential, Magnetic properties, and 21 ACS Paragon Plus Environment


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Page 22 of 33

492

TGA) for the prepared adsorbent, Physicochemical properties of real environmental samples,

493

percentage distribution of U(VI) and NTMP ligand and the comparison of the synthesized

494

adsorbent with other adsorbents.

495

This material is available free of charge via the Internet at http://pubs.acs.org.

496 497 498 499 500 501 502 503 504

References

505

1.

506

and groundwater resources: a review. Crit. Rev. Env. Sci. Tec. 2015, 45 (22), 2391-2423; DOI

507

10.1080/10643389.2015.1025642.

508

2.

509

techniques for uranium (VI) ion retrieval from contaminated aqueous environment. J. Environ. Chem.

510

Eng. 2014, 2 (3), 1621-1634; DOI 10.1016/j.jece.2014.06.007.

511

3.

512

10.1126/science.151.3707.172.

513

4.

514

mini review of available treatment methods. Desalin. Water Treat. 2013, 51 (13-15), 2915-2925; DOI

515

10.1080/19443994.2012.748300.

516

5.

517

Health 2011, 26 (4), 231-249; DOI 10.1515/REVEH.2011.032.

Waseem, A.; Ullah, H.; Rauf, M. K.; Ahmad, I., Distribution of natural uranium in surface

Bhalara, P. D.; Punetha, D.; Balasubramanian, K., A review of potential remediation

Pearson, R. G., Acids and Bases. Science 1966, 151, (3707), 172-177; DOI:

Katsoyiannis, I.; Zouboulis, A., Removal of uranium from contaminated drinking water: a

Brugge, D.; Buchner, V., Health effects of uranium: new research findings. Rev. Environ.


Page 23 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


518

6.

519

Dissanayake, C., Natural radionuclides and trace elements in rice field soils in relation to fertilizer

520

application: study of a chronic kidney disease area in Sri Lanka. Environ. Earth Sci. 2010, 60 (1),

521

193-201; DOI 10.1007/s12665-009-0179-1.

522

7.

523

Wilkerson, R. C.; Vena, J. E.; Hébert, J. R., Groundwater uranium and cancer incidence in South

524

Carolina. Cancer Cause. Control 2011, 22 (1), 41-50; DOI 10.1007/s10552-010-9669-4.

525

8.

526

Marion, S. L.; Begay, C.; Propper, C. R.; Hoyer, P. B., Drinking water with uranium below the US

527

EPA water standard causes estrogen receptor-dependent responses in female mice. Environ. Health

528

Persp. 2007, 115 (12), 1711-1716; DOI 10.1289/ehp.9910.

529

9.

530

Sachde, D., Recovery of uranium from seawater: A review of current status and future research needs.

531

Separ. Sci. Technol. 2013, 48 (3), 367-387; DOI 10.1080/01496395.2012.712599.

532

10.

533

of uranium (VI) with diamides of dipicolinic acid from nitric acid solutions. Radiochim. Acta 2009,

534

97 (6), 291-296; DOI 10.1524/ract.2009.1588.

535

11.

536

and radium from a natural water. Water, Air, Soil Pollut. 2006, 173 (1-4), 57-69; DOI

537

10.1007/s11270-005-9026-5.

538

12.

539

behaviour of uranium in submerged ultrafiltration. J. Membrane Sci, 2010, 348 (1), 174-180; DOI

540

10.1016/j.memsci.2009.10.056.

541

13.

542

Am. Chem. Soc. 2015, 137 (8), 2788-2791; DOI 10.1021/ja510488r.

543

14.

544

Am. Chem. Soc. 2012, 134 (39), 16441-16446; DOI 10.1021/ja308028n.

Chandrajith, R.; Seneviratna, S.; Wickramaarachchi, K.; Attanayake, T.; Aturaliya, T.;

Wagner, S. E.; Burch, J. B.; Bottai, M.; Puett, R.; Porter, D.; Bolick-Aldrich, S.; Temples, T.;

Raymond-Whish, S.; Mayer, L. P.; O'Neal, T.; Martinez, A.; Sellers, M. A.; Christian, P. J.;

Kim, J.; Tsouris, C.; Mayes, R. T.; Oyola, Y.; Saito, T.; Janke, C. J.; Dai, S.; Schneider, E.;

Lapka, J.; Paulenova, A.; Alyapyshev, M. Y.; Babain, V.; Herbst, R.; Law, J. D., Extraction

Baeza, A.; Fernandez, M.; Herranz, M.; Legarda, F.; Miro, C.; Salas, A., Removing uranium

Semião, A. J.; Rossiter, H. M.; Schäfer, A. I., Impact of organic matter and speciation on the

Ling, L.; Zhang, W.-x., Enrichment and encapsulation of uranium with iron nanoparticle. J.

Manos, M. J.; Kanatzidis, M. G., Layered metal sulfides capture uranium from seawater. J.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

545

15.

546

assisted chemical separation. Separ. Sci. Technol. 1995, 30 (7-9), 1455-1471; DOI

547

10.1080/01496399508010357.

548

16.

549

magnetic particles for the extraction and separation of lanthanides and actinides from nuclear waste

550

streams. J. Magn. Magn. Mater. 2006, 301 (2), 312-318; DOI 10.1016/j.jmmm.2005.07.005.

551

17.

552

with extractant-coated magnetic microparticles. Separ. Sci. Technol. 2000, 35 (13), 2003-2018; DOI

553

10.1081/SS-100102086.

554

18.

555

adsorbed onto superparamagnetic carriers. J. Magn. Magn. Mater. 1999, 194 (1), 102-107; DOI

556

10.1016/S0304-8853(98)00571-X.

557

19.

558

coating process of organic actinide extractants on magnetically assisted chemical separation particles.

559

Sep. Purif. Technol. 1997, 11 (3), 211-219; DOI 10.1016/S1383-5866(97)00022-1.

560

20.

561

dibutyl tetradecyl malonamide impregnated magnetic particles for the extraction and separation of

562

radionuclides from nuclear waste streams. Radiochim. Acta 2006, 94 (5/2006), 267-273. DOI

563

10.1524/ract.2006.94.5.267.

564

21.

565

Actinide Specific Chelator for Radioactive Waste Separation. Environ. Sci. Technol. 2013, 47 (21),

566

11942-11959; DOI 10.1021/es402205q.

567

22.

568

heating of discrete droplets using magnetic porous silicon-based photonic crystals. J. Am. Chem. Soc.

569

2006, 128 (24), 7938-7946; DOI 10.1021/ja0612854.

570

23.

571

adsorbent based on mesoporous carbon for sequestration of radioactive Cesium. Chem. Eng. J. 2017,

572

308, 798-808; DOI 10.1016/j.cej.2016.09.116.

Nuñez, L.; Buchholz, B.; Vandegrift, G., Waste remediation using in situ magnetically

Shaibu, B.; Reddy, M.; Bhattacharyya, A.; Manchanda, V., Evaluation of Cyanex 923-coated

Kaminski, M.; Nunez, L., Separation of uranium from nitric-and hydrochloric-acid solutions

Nuñez, L.; Kaminski, M. D., Transuranic separation using organophosphorus extractants

Buchholz, B.; Tuazon, H.; Kaminski, M.; Aase, S.; Nufiez, L.; Vandegrift, G., Optimizing the

Shaibu, B.; Reddy, M.; Prabhu, D.; Kanekar, A.; Manchanda, V., N, N′-dimethyl-N, N′-

Kaur, M.; Zhang, H.; Martin, L.; Todd, T.; Qiang, Y., Conjugates of Magnetic Nanoparticle

Park, J.-H.; Derfus, A. M.; Segal, E.; Vecchio, K. S.; Bhatia, S. N.; Sailor, M. J., Local

Husnain, S. M.; Um, W.; Chang, Y.-Y.; Chang, Y.-S., Recyclable superparamagnetic


Page 25 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


573

24.

574

Luminescent Magnetic Mesoporous Carbon Nanospheres for Controlled Release of Anticancer Drug

575

and Multimodal Imaging. Langmuir 2016, 32 (6), 1611-1620; DOI 10.1021/acs.langmuir.5b03898.

576

25.

577

confined within ordered mesoporous carbons as efficient microwave absorbers. Phys. Chem. Chem.

578

Phys. 2015, 17 (5), 3802-3812; DOI 10.1039/C4CP04228J.

579

26.

580

carbon microspheres for rapid capture of low-concentration peptides. ACS Appl. Mater. Interfaces

581

2014, 6 (15), 12719-12728; DOI 10.1021/am502712a.

582

27.

583

A.; Zhao, D., Templated fabrication of core–shell magnetic mesoporous carbon microspheres in 3-

584

dimensional ordered macroporous silicas. Chem. Mater. 2014, 26 (10), 3316-3321; DOI

585

10.1021/cm501186e.

586

28.

587

efficient removal of organic pollutants. Adsorption 2012, 18 (5-6), 439-444; DOI 10.1007/s10450-

588

012-9430-2.

589

29.

590

uranium (VI) using oxime-grafted ordered mesoporous carbon CMK-5. J. Hazard. Mater. 2011, 190

591

(1), 442-450 DOI 10.1016/j.jhazmat.2011.03.066.

592

30.

593

sorption with functionalized mesoporous carbon materials. Ind. Eng. Chem. Res. 2013, 52 (43),

594

15187-15197; DOI 10.1021/ie402646r.

595

31.

596

from aqueous solution by the carboxyl-mesoporous carbon. Chem. Eng. J. 2012, 198, 246-253; DOI

597

10.1016/j.cej.2012.05.112.

598

32.

599

Chem. 1958, 62 (5), 590-593; DOI 10.1021/j150563a017.

Mohapatra, S.; Rout, S. R.; Das, R. K.; Nayak, S.; Ghosh, S. K., Highly Hydrophilic

Wang, J.; Zhou, H.; Zhuang, J.; Liu, Q., Magnetic γ-Fe 2 O 3, Fe 3 O 4, and Fe nanoparticles

Cheng, G.; Zhou, M.-D.; Zheng, S.-Y., Facile synthesis of magnetic mesoporous hollow

Wang, M.; Wang, X.; Yue, Q.; Zhang, Y.; Wang, C.; Chen, J.; Cai, H.; Lu, H.; Elzatahry, A.

Wang, T.; Liang, L.; Wang, R.; Jiang, Y.; Lin, K.; Sun, J., Magnetic mesoporous carbon for

Tian, G.; Geng, J.; Jin, Y.; Wang, C.; Li, S.; Chen, Z.; Wang, H.; Zhao, Y.; Li, S., Sorption of

Carboni, M. l.; Abney, C. W.; Taylor-Pashow, K. M.; Vivero-Escoto, J. L.; Lin, W., Uranium

Wang, Y.-Q.; Zhang, Z.-B.; Liu, Y.-H.; Cao, X.-H.; Liu, Y.-T.; Li, Q., Adsorption of U (VI)

Burger, L., Uranium and plutonium extraction by organophosphorus compounds. J. Phys.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 33

600

33.

601

molecules for the control of surface/interface properties and the synthesis of nanomaterials. Dalton

602

Trans. 2013, 42 (35), 12569-12585; DOI 10.1039/C3DT51193F.

603

34.

604

complexing agent in sorption of heavy metal ions on ion exchangers. Chem. Eng. J. 2013, 215, 948-

605

958; DOI 10.1016/j.cej.2012.10.054.

606

35.

607

copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous

608

silica structures. J. Am. Chem. Soc. 1998, 120, (24), 6024-6036; DOI 10.1021/ja974025i.

609

36.

610

surfaces modified by Langmuir-Blodgett monolayers using sum-frequency vibrational spectroscopy

611

and X-ray photoelectron spectroscopy. J. Phys. Chem. B 2006, 110 (17), 8701-8714; DOI

612

10.1021/jp057180p.

613

37.

614

carbon as a novel solid acid catalyst for the esterification of oleic acid. Catal. Commun. 2014, 56,

615

164-167; DOI 10.1016/j.catcom.2014.07.008.

616

38.

617

electrochemical characterization of pitting corrosion behaviour of 304 stainless steel in ground water

618

media. J. Appl. Electrochem. 2007, 37 (4), 439-449; DOI 10.1007/s10800-006-9274-0.

619

39.

620

of an alkyl N-aminodimethylphosphonate on steel: An XPS study. Appl. Surf. Sci. 2006, 252 (8),

621

2757-2769; DOI 10.1016/j.apsusc.2005.04.012.

622

40.

623

anchoring on magnetic Fe3O4 nanoparticles modified with phosphonic linkers. Eur. J. Inorg. Chem.

624

2012, 2012 (32), 5323-5331; DOI 10.1002/ejic.201200510.

625

41.

626

radioactive material from the Fukushima nuclear accident. Sci. Rep. 2014, 4, 6053; DOI

627

10.1038/srep06053.

Guerrero, G.; Alauzun, J. G.; Granier, M.; Laurencin, D.; Mutin, P. H., Phosphonate coupling

Kołodyńska, D.; Gęca, M.; Siek, M.; Hubicki, Z., Nitrilotris (methylenephosphonic) acid as a

Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D., Nonionic triblock and star diblock

Keszthelyi, T.; Pászti, Z.; Rigó, T.; Hakkel, O.; Telegdi, J.; Guczi, L., Investigation of solid

Wang, L.; Dong, X.; Jiang, H.; Li, G.; Zhang, M., Phosphorylated ordered mesoporous

Gopi, D.; Manimozhi, S.; Govindaraju, K.; Manisankar, P.; Rajeswari, S., Surface and

Frateur, I.; Carnot, A.; Zanna, S.; Marcus, P., Role of pH and calcium ions in the adsorption

Tudisco, C.; Oliveri, V.; Cantarella, M.; Vecchio, G.; Condorelli, G. G., Cyclodextrin

Yamaguchi, D.; Furukawa, K.; Takasuga, M.; Watanabe, K., A magnetic carbon sorbent for


Page 27 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


628

42.

629

for high efficient removal of heavy metals in water. Environ. Sci. Technol. 2008, 42 (18), 6949-6954;

630

DOI 10.1021/es800924c.

631

43.

632

mesoporous carbon functionalized with carboxylate groups and magnetic nanoparticles as a promising

633

adsorbent. J. Colloid Interface Sci. 2012, 369 (1), 366-372; DOI 10.1016/j.jcis.2011.12.051.

634

44.

635

“Stereoscopic” 2D super-microporous phosphazene-based covalent organic framework: Design,

636

synthesis and selective sorption towards uranium at high acidic condition. J. Hazard. Mater. 2016,

637

314, 95-104; DOI 10.1016/j.jhazmat.2016.04.031.

638

45.

639

Functionalized magnetic mesoporous silica nanoparticles for U removal from low and high pH

640

groundwater. J. Hazard. Mater. 2016, 317, 494-502; DOI 10.1016/j.jhazmat.2016.05.093.

641

46.

642

Yang, X., Efficient uranium capture by polysulfide/layered double hydroxide composites. J. Am.

643

Chem. Soc. 2015, 137 (10), 3670-3677; DOI 10.1021/jacs.5b00762.

644

47.

645

trialkylphosphine-oxide extraction. Nucl. Technol. 1994, 108 (3), 361-369.

646

48.

647

performance of phosphonate-functionalized mesoporous silica for U (VI) sorption from aqueous

648

solution. Dalton Trans. 2011, 40 (28), 7446-7453; DOI 10.1039/c1dt10085h.·

649

49.

650

Prussian blue/graphene oxide nanocomposites for removal of radioactive cesium in water. J. Mater.

651

Chem. A 2014, 2 (2), 326-332; DOI 10.1039/C3TA13548A.

652

50.

653

different U (VI) sequestration processes. Geochim. Cosmochim. Acta 2009, 73 (20), 5989-6007; DOI

654

10.1016/j.gca.2009.07.002.

Liu, J.-F.; Zhao, Z.-s.; Jiang, G.-b., Coating Fe3O4 magnetic nanoparticles with humic acid

Chi, Y.; Geng, W.; Zhao, L.; Yan, X.; Yuan, Q.; Li, N.; Li, X., Comprehensive study of

Zhang, S.; Zhao, X.; Li, B.; Bai, C.; Li, Y.; Wang, L.; Wen, R.; Zhang, M.; Ma, L.; Li, S.,

Li, D.; Egodawatte, S.; Kaplan, D. I.; Larsen, S. C.; Serkiz, S. M.; Seaman, J. C.,

Ma, S.; Huang, L.; Ma, L.; Shim, Y.; Islam, S. M.; Wang, P.; Zhao, L.-D.; Wang, S.; Sun, G.;

Zhu, Y.; Jiao, R., Chinese experience in the removal of actinides from highly active waste by

Yuan, L.-Y.; Liu, Y.-L.; Shi, W.-Q.; Lv, Y.-L.; Lan, J.-H.; Zhao, Y.-L.; Chai, Z.-F., High

Yang, H.; Sun, L.; Zhai, J.; Li, H.; Zhao, Y.; Yu, H., In situ controllable synthesis of magnetic

Singer, D. M.; Maher, K.; Brown, G. E., Uranyl–chlorite sorption/desorption: Evaluation of



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 33

655

51.

656

arenes for Uranyl Extraction. Chinese J. Chem. 2015, 33 (3), 361-367; DOI 10.1002/cjoc.201400899.

657

52.

658

characterization of tributyl phosphate grafted carbon nanotubes by the floating catalytic chemical

659

vapor deposition method and their sorption behavior towards uranium. New J. Chem. 2016, 40 (2),

660

1213-1221; DOI 10.1039/C5NJ02639C.

661

53.

662

valent iron. J. Environ. Radioact. 2016, 164, 65-72; DOI 10.1016/j.jenvrad.2016.06.027.

663

54.

664

for the removal of radioactive minerals from real mine water. J. Environ. Radioact. 2016, 164, 369-

665

376; DOI 10.1016/j.jenvrad.2016.08.014.

666

55.

667

acid mine water using strong base resins. J. Hazard. Mater. 2007, 148 (3), 499-504; DOI

668

10.1016/j.jhazmat.2007.03.003.

669

56.

670

and graphene oxide. Chem. Res. Toxicol. 2014, 27 (2), 159-168; DOI 10.1021/tx400385x.

671

57.

672

x S 8− x (x= 0.65–1): a new metal sulfide for rapid and selective removal of Cs+, Sr 2+ and UO 2 2+

673

ions. Chem. Sci. 2016, 7 (2), 1121-1132; DOI 10.1039/C5SC03040D.

674

58.

675

Removal and Recovery of Uranium by a Layered Organic-Inorganic Hybrid Thiostannate. J. Am.

676

Chem. Soc. 2016, 138 (38), 125787-12585; DOI 10.1021/jacs.6b07351.

677

59.

678

Synthesis of phytic acid-decorated titanate nanotubes for high efficient and high selective removal of

679

U (VI). Chem. Eng. J. 2017, 322, 353-365; DOI 10.1016/j.cej.2017.03.156.

Bai, B.; Fang, Y.; Gan, Q.; Yang, Y.; Yuan, L.; Feng, W., Phosphorous‐Based Pillar [5]

Mishra, S.; Dwivedi, J.; Kumar, A.; Sankararamakrishnan, N., The synthesis and

Jing, C.; Li, Y.; Landsberger, S., Review of soluble uranium removal by nanoscale zero

Oyewo, O. A.; Onyango, M. S.; Wolkersdorfer, C., Application of banana peels nanosorbent

Ladeira, A. C. Q.; Gonçalves, C. R., Influence of anionic species on uranium separation from

Seabra, A. B.; Paula, A. J.; de Lima, R.; Alves, O. L.; Duran, N., Nanotoxicity of graphene

Sarma, D.; Malliakas, C. D.; Subrahmanyam, K.; Islam, S. M.; Kanatzidis, M. G., K 2x Sn 4−

Feng, M.-L.; Sarma, D.; Qi, X.; Du, K.-Z.; Huang, X.-Y.; Kanatzidis, M. G., Efficient

Yuan, F.; Wu, C.; Cai, Y.; Zhang, L.; Wang, J.; Chen, L.; Wang, X.; Yang, S.; Wang, S.,


Page 29 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


680

60.

681

L., Overcoming the crystallization and designability issues in the ultrastable zirconium phosphonate

682

framework system. Nat. Commun. 2017, 8, 15369; DOI 10.1038/ncomms15369.

683

61.

684

Performance and Mechanism of Uranium Adsorption from Seawater to Poly (dopamine)-Inspired

685

Sorbents. Environ. Sci. Technol. 2017, 51 (8), 4606-4614; DOI 10.1021/acs.est.7b00470.

Zheng, T.; Yang, Z.; Gui, D.; Liu, Z.; Wang, X.; Dai, X.; Liu, S.; Zhang, L.; Gao, Y.; Chen,

Wu, F.; Pu, N.; Ye, G.; Sun, T.; Wang, Z.; Song, Y.; Wang, W.; Huo, X.; Lu, Y.; Chen, J.,

686 687 688 689 690

Figure Captions

691

Figure 1 (a,b) TEM of CMK-3 and P-CMK-3, (c,d) TEM and (e) HR-TEM images of P-Fe-

692

CMK-3 adsorbent.

693

Figure 2. (a) UO22+ adsorption comparison among different mesoporous carbon adsorbents;

694

(b) Effect of contact time on UO22+ adsorption by P-Fe-CMK-3 and corresponding kinetic

695

parameters; Effects of solution pH (c) and ionic strength (d) on UO22+ adsorption by P-Fe-

696

CMK-3; (e) Langmuir and Freundlich isotherms curve fitting and corresponding parameters

697

for UO22+ adsorption by P-Fe-CMK-3; (f) Reactivity comparison among heavy metals (inset,

698

selectivity coefficient for uranyl ions realative to competing ions)

699

Figure 3. (a) FE-SEM EDS analysis and elemental mapping; (b) XPS survey scan of UO22+-

700

adsorbed P-Fe-CMK-3; High resolution deconvoluted XPS of U 4f (c), P 2p (d) and N 1s (e).

701

Figure 4. (a) Proposed removal mechanism of UO22+ on P-Fe-CMK-3; (b) UO22+ adsorption

702

performance over five regeneration cycles on P-Fe-CMK-3 with initial UO22+ concentration

703

of 2.2 ppm.

704



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 33

705 706 707 708 709 710

711 712 713 714 715

Figure 1 (a,b) TEM of CMK-3 and P-CMK-3, (c,d) TEM and (e) HR-TEM images of P-Fe-

716

CMK-3 adsorbent.

717 718 30 ACS Paragon Plus Environment

Page 31 of 33

amount of UO2+ adsorbed (mg g-1) 2

adsorbed UO2+ (mg g-1) 2

719 720

a

80

60

40

20

60

CMK-3

b

50

Experimental Pseudo I order Pseudo II order

40 30

Pseudo I parameters qe (mg g-1) k1(mg g-1) R2 56 1.30 0.94 Pseudo II parameters -1 -1 -1 qe (mg g ) k2(g mg min ) R2 57.93 0.03 0.98

20 10

0

Fe-CMK-3 P-Fe-CMK-3 P-CMK-3

50

100

4

80

10

60

10

40

102

20

101

0

0

3

1M

1.1

2

3.68

4.75

6.48

d

40 30 20 10

0

1

10

100

500

1000

Concentration of NaCl (mM)

140

1.0E4

e

200

Langmuir parameters KL (L g-1)

Qm (mg g-1)

R2

0.029

150±4.70

0.973

2+ 2

SUO

Kd (mL g-1)

Experimental Langmuir Freundlich

100

/M n+

8.0E3

80

f

250

120

6.0E3

150 100 50

4.0E3 2+ Pb2+ Cd Cr6+ Cu2+ Ni2+

Freundlich parameters

60

n

KF (mg g -1)

R2

3.4

26±2.50

0.98

Hg2+ As5+ Zn2+

2.0E3

40

0.0

0

723

250

50

Acidity / Final pH

722

200

0

10

2M

150

60

adsorbed UO2+ (mg g-1) 2

Capacity Kd

Kd (mL g-1)

Adsorption capacity (mg g-1)

105

c

58

Time (min)

721 100

Saturation Capacity qe (mg g-1)

0

0

Qe (mg g-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

200 Ce (mg L-1)

300

6+

2+ UO2+ Cr Pb2+ Cd 2

Cu2+ Ni2+ Hg2+

2+ As5+ Zn

724

Figure 2. (a) UO22+ adsorption comparison among different mesoporous carbon adsorbents;

725

(b) Effect of contact time on UO22+ adsorption by P-Fe-CMK-3 and corresponding kinetic

726

parameters; Effects of solution pH (c) and ionic strength (d) on UO22+ adsorption by P-Fe-

727

CMK-3; (e) Langmuir and Freundlich isotherms curve fitting and corresponding parameters

728

for UO22+ adsorption by P-Fe-CMK-3; (f) Reactivity comparison among heavy metals (inset,

729

selectivity coefficient for uranyl ions realative to competing ions)

730



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 33

731 732 733

a

734 735 736 737

738

c

U-P-Fe-CMK-3

739

C 1s

O 1s

740 Fe 2p

N 1s

U 4f

741

P 2s P 2p

800

600

400

200

0

B.E (eV)

742

d

e

743 744 745 746 747


Page 33 of 33

748

Figure 3. (a) FE-SEM EDS analysis and elemental mapping; (b) XPS survey scan of UO22+-

749

adsorbed P-Fe-CMK-3; High resolution deconvoluted XPS of U 4f (c), P 2p (d) and N 1s (e).

750 751 752 753 754 755

a

HO

O

P

756

C M

N P

O

C

758

O

P

O

M

OH

757

C

759 760

OH

HO

M

b

100

761 762 763

% UO2+ adsoprtion 2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

764 765

0

1

2

3

4

5

Cycle

766 767

Figure 4. (a) Proposed removal mechanism of UO22+ on P-Fe-CMK-3; (b) UO22+ adsorption

768

performance over five regeneration cycles on P-Fe-CMK-3 with initial UO22+ concentration

769

of 2.2 ppm.


Superparamagnetic Adsorbent Based on Phosphonate Grafted

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